1. Field
Embodiments described herein relate generally to a semiconductor memory device.
2. Description of the Related Art
Recently, resistance varying memory device using a variable resistance element as its memory element has been paid attention as a candidate to succeed flash memory. A memory cell of a resistance varying memory device includes a variable resistance material between two electrodes, and the variable resistance material is set to a high resistance state and a low resistance state by control of the polarity of a voltage to be applied, the voltage value, the time for which the voltage is applied, etc.
In order to increase the memory capacity of a resistance varying memory device, there is known a configuration of storing information of two bits or more in one memory cell by connecting three or more electrodes to a memory cell and controlling the resistance state of the variable resistance element minutely. However, a memory element to which three or more electrodes are to be connected will have a complicated connection relationship with the electrodes, making it difficult to increase the number of electrodes. Moreover, there is a problem in increasing the number of electrodes, because this increases the area of a memory cell and hence makes it difficult to increase the memory capacity per unit area.